The invention relates to an improvement of the so-called internal magnet type magnetron in which permanent magnets are disposed in an evacuated envelope hermetically sealed and, more particularly, to an improvement of the microwave output section of that type magnetron.
The internal magnet type magnetron has a good efficiency with respect to magnetic energy, compared with outer magnet type magnetrons in which the permanent magnets are disposed outside the evacuated envelope, in which magnetic energy may effectively be introduced from the magnets to an interaction space of the magnetron. The internal magnet type magnetron also have other advantages: is compact, the structure is simple and the cost is low. Although having such advantages, internal magnet type magnetrons have some problems at the experimental stage. One of them is that it is impossible to effectively transfer high frequency energy generated in a space defined by vanes and the cathode in an anode cylinder an output section, i.e., the output antenna. A possible cause of the problem is that the output antenna is weakly coupled with a vane in the oscillating reagion. Measurements show that only 30% of the generated high frequency energy is transmitted to the output section. Another problem is that electromagnetic energy of undesired modes is generated in the space around the permanent magnet and is transferred to the antenna, in addition to the predetermined electromagnetic energy. This arises from the structure of the internal magnet type magnetron, specifically that the output conductor extending from the vane to the antenna passes through an electromagnetic field having undesired modes in the space around the permanent magnet in the anode cylinder.